A diamond obtained by an impact pressure, explosive bombardment method (impact method) using an oxygen-deficient explosive, such as trinitrotoluene (TNT) or hexogen (RDX), is referred to as nanodiamond (ND), since the primary particles are extremely small to be 3-20 nm (e.g., Non-patent Publication 1 and Non-patent Publication 2). Due to its nanoscale particle size, ND is expected to be utilized in a wide use, besides normal diamond uses, such as abrasive, lubricant, heat-exchange fluid medium, composite materials with resin, metal, etc., electronic materials such as low dielectric film, emitter material, etc., and a medical field such as DNA support, virus-capturing support, etc. In the case of industrially using ND for the purpose of such use, it is requested to provide ND as a dispersion liquid in which fine particles of less than 100 nm are dispersed in liquid. However, since an impurity carbon layer, such as non-graphite and graphite films, is fused on the ND fine particle surface, and since ND is produced normally as secondary and tertiary aggregates having a particle size of 50-7500 nm as it is also referred to as cluster diamond (CD), it is necessary to conduct the removal of the impurity carbon layer of these and the pulverization of the aggregates. Furthermore, in the case of handling nano-level order particles by dispersing them in a solution, aggregation among particles tends to occur more easily if they are smaller particles, and the aggregated particles precipitate. Therefore, it is very difficult to obtain a stable dispersion liquid. Thus, as a means for solving these problems, a method for stably dispersing ND in liquid in primary particles with a bead-mill wet pulverizer, an ultrasonic homogenizer, etc. is variously studied (e.g., Patent Publication 1 and Patent Publication 2).
Furthermore, there is also reported a method of reacting CD with fluorine gas for the purpose of pulverizing secondary and tertiary ND aggregates (CD). For example, when CD is brought into contact with fluorine with a reaction temperature of 300-500° C., a fluorine gas pressure of 0.1 MPa, and a reaction time of 5-10 days, a fluorinated CD having a F/C molar ratio of about 0.2 (XPS, elementary analysis) is obtained, while maintaining the diamond structure (Non-patent Publication 3). It has been observed by TEM that this fluorine treatment makes a CD of a secondary particle diameter of about 40 μm have about 200 nm by a partial relaxation of the aggregation. Furthermore, it has been confirmed that CD friction coefficient extremely lowers by a rotary-type friction test using a mixed powder with polytetrafluoroethylene (PTFE) (Non-patent Publication 4). It has been reported that this was caused by that the non-graphite carbon on the ND surface had been removed by the reaction at a high temperature, and that the surface energy had lowered by the formation of CF group, CF2 group, CF3 group, etc. on the ND surface, as a ND lattice pattern by the TEM observation is evident (Non-patent Publication 5). Furthermore, there has also been reported that a synthesis of a fluorinated ND having a fluorine content of 5-8.6 at. % (analysis by EDX) by a fluorine treatment with reaction temperatures of 150, 310, 410 and 470° C., a F2/H2 flow rate ratio of 3/1, and a reaction time of 48 hours has brought a result of the improvement of dissolution in a polar solvent, such as ethanol, as compared with the original ND (Non-patent Publication 6 and Patent Publication 3). It is, however, difficult to completely pulverize the whole of the CD aggregates by this fluorination treatment. Therefore, in the case of obtaining a dispersion liquid in which a nano-order fluorinated ND having a particle size of less than 100 nm is dispersed, it is essential to conduct a classification operation, such as centrifugation treatment or filter filtration, after conducting a dispersion treatment with an ultrasonic homogenizer or the like. This classification operation lowers the concentration of a fluorinated ND to be dispersed. Therefore, it is necessary to conduct a step such as concentration to obtain a dispersion liquid in which a fluorinated ND is dispersed at a high concentration.    Patent Publication 1: JP-A-2005-1983    Patent Publication 2: JP-A-2005-97375    Patent Publication 3: US 2005/0158549 A1 specification    Non-patent Publication 1: Eiji OSAWA: Journal of the Japan Society for Abrasive Technology, 47, 414 (2003).    Non-patent Publication 2: Kotaro HANADA: Journal of the Japan Society for Abrasive Technology, 47, 422 (2003).    Non-patent Publication 3: Tatsumi OHI, Akiko YONEMOTO, Shinji KAWASAKI, Fujio OKINO, and Hidekazu TOUHARA: Abstract of the 26th Fluorine Conference of Japan (November, 2002) p. 24-25    Non-patent Publication 4: Akiko YONEMOTO, Tatumi OHI, Shinji KAWASAKI, Fujio OKINO, Fumiaki KATAOKA, Eiji OSAWA, and Hidekazu TOUHARA: Abstract of the 83rd Spring Annual Meeting of the Chemical Society of Japan (March, 2003), p. 101.    Non-patent Publication 5: H. Touhara, K. Komatsu, T. Ohi, A. Yonemoto, S. Kawasaki, F. Okino and H. Kataura: Third French-Japanese Seminar on Fluorine in Inorganic Chemistry and Electrochemistry (April, 2003).    Non-patent Publication 6: Y. Liu, Z. Gu, J. L. Margrave, and V. Khabashesku; Chem. Mater. 16, 3924 (2004).